As display devices which are usable for electric appliances and electronic devices, a liquid crystal display device using an electro-optical effect of a liquid crystal material and an organic EL (electroluminescence) display device including an organic electroluminescence (EL) element have been developed. Especially, a display device including an organic EL element used as a display element has a wide viewing angle and provides high definition display.
It is known that in the case where an organic EL element is used as a display element, an organic EL layer is deteriorated by moisture. When the display device is driven by use of such a deteriorated organic EL layer, the luminance may be decreased or a display failure may occur. In order to prevent the organic EL layer from being contaminated with moisture, a sealing layer is provided. Japanese Laid-Open Patent Publication No. 2015-65025 discloses a sealing layer including a stack of an inorganic insulating layer, an organic insulating layer and an inorganic insulating layer.